For electrooptical display elements whose operation is based on the phenomenon of dynamic scattering, deformation of oriented phases (DOP effect) or absorption of light by orientatable dichroic dyestuffs, liquid crystal dielectrics are required which have a significant negative dielectric anisotropy (DCA) and in which the dielectric constant (DC) parallel to the molecular axis is smaller than the DC perpendicular to the molecular axis. The more negative the DCA of the liquid crystal dielectric is, the smaller is the threshold voltage for operation of such display elements. A further basic requirement of such dielectrics is a broad temperature range for the nematic phase, including room temperature.
Of the customary liquid crystal base materials of such dielectrics, there is none with a markedly negative DCA. In order to prepare liquid crystal dielectrics with a marked negative DCA using these materials, it is necessary to add liquid crystal compounds having a very highly negative DCA. These compounds are usually insufficiently soluble in the liquid crystal base materials, are unstable as esters, and/or cause an undesirable shift in the nematic temperature range. If need be, the solubility problems can be solved by using several compounds having a negative DCA, but this is accomplished at the expense of an increase in the viscosity of the nematic phase and the resulting undesirable increase in the switching times of the display element.